Enel, the partly state-owned Italian utility group, was confident last night of building a stake of just under 25 per cent in Endesa, in a move that could derail a €41bn ($54bn) takeover bid by Germany's Eon for Spain's largest electricity company.

Eon said it would not withdraw its bid, tabled last month after a 12-month battle with Spanish regulators, politicians and blocking shareholder groups.